Method of preparing gels for catalytic and adsorbent purposes



Patented Mar. 16, 1926.

UNHTED STATES 1,577,190 PATENT OFFICE.

WALTER A. PATRICK, 01 5 BALTIMORE, MARYLAND.

METHOD OF PREPARING GELS FOR CATALYTIC AND ADSOTIIBENT PURPOSES.

No Drawing. Original application filed February 28, 1920, Serial No. 862,138. Divided and this ap plication filed May 24, 1924. Serial llo. 715,731.

To all whom it may concern:

Be it known that I, 'WAL'mR A. PATRICK, a citizen ofthe United States, and residing at Baltimore, State of Maryland, haveinvented certain new and useful Improvements in Methods of PreparingGels for Catalytic and Adsorbent Purposes, of which the following is a specification.

The present invention, which is a division of my application 362,138 filed Feb. 28, 1920, relates to adsorbent gels having chemically active or catalytic agents associated therewith.

In my Patent No. 1,297,724 I have disclosed the method ofmaking a hard highly porous silica gel stable up to 700 centigrade having ultra microscopic pores. It is the principal object of the present invention to produce gels similar in physical structure to the gel described in the above mentioned patent, but which possess special properties due to the incorporation of other substances.

The present invention comprehends els of hard, stable porous structure having u tra microscopic pores and also having associated therewith one or more members of the class of catalyzers containing metallic elements.

From a chemical standpoint it is very desirable to have certain substances in a physical structure similar to that of a porous gel such as silica gel described in the aforesaid patent. Silica is an inert substance chemically and for thisreason is admirably suited for adsorbing and recovering gases and vapors, provided of course that it is given the proper structure. On the other hand, other substances, such as certain metallic oxides and metals are known to possess desirable chemical and catalytic properties. If these metals and metallic oxides can be obtained with a structure similar to that, of the gel described in the patent, the above properties are enhanced and made more active, because of the large surface presented. According to the present invention it is possible to obtain a gel of the structure disclosed 1n the patent having one or more of the members of the class of catalyzers containing metallic elements incorporated therewith.

In the preparation of silica gel as described in the patent, use is made of the reaction between a soluble silicate and an acid to produce colloidal silicic acid. It 1s found necessary to allow the silicic acid to set to a hydrogel in a medium of certain definite acid concentration in order to insure a gel of the proper structure. The concentration oi. the acid is from about three-tenths to nine-tenths gram ions of hydrogen per litre, the preferred concentration being about fivetenths gram ions of hydrogen per litre.

One method, which is claimed in said application 362,138 utilizes hydrolysis of metall c salts to secure the proper acid concentration for the setting of the colloidal silicic acid. For example, if a solution of water glass of the proper concentration be mixed with asolution of ferric chloride, the mixture will set to a hydrogel, which can be washed free of chlorides withsubstantially no loss of iron, and the resulting hydrogel when dried as described in mypatent, is

found to consist of a mixture of silica and ferric oxide, together with the usual quantity of water. Wide variation of the ratio of ferric oxide to silica may be obtained by proper selection of the concentrations and volumes of water glass and ferric chloride solutions. The resulting gel adsorbs gases and vapors, with which it does not interact chemically to the same degree as the plain silica gel of the patent. On the other hand, the addition of the ferric oxide increases the power of the gel for adsorption of gases and vapors with-which it may chemically combine. The iron oxide also adds catalytic properties to the gel. For example, the reaction between sulphurdioxide and oxygen is markedly catalyzed by the mixture of Fe O and SiO,,, while the silica gel itself is without effect on the velocity of the above reaction.

It is possible to secure a great number of mixtures of metallic oxides with silica and similar substances by the application of the above principle. Thus aluminum oxide may be obtained intermixed with silica possessing a gel structure, providing proper solutions of aluminum chloride and water glass The dried gel will be Fe O CuO SiO Fe O MgO SiO Fe O CdO SiO Fe O ZnO SiO Fe O Mn O SiO A1 0 CuO SiO The present application comprehends a method of preparlng gels of metallic salts that are not as easily hydrol zed in water as the above, it being found hat upon setting of the hydrogel, it is possible to wash the material free of the acid radical, thereby completing the hydrolysis. This action has been explained by F. G. Donnan in his papers on Membrane permeability published in volume 2 of System of Physical Chemistry by W. C. McLewis, page 275. For example, if a mixture of copper chloride, Water-glass and hydrochloric acid be prepared of such a nature that the whole will set to a hydrogel, it is found that it is pos sible to entirely free the mixture of chlorides by washing without loss of muchcopper. The loss of copper in the washing depends upon the amount of acid used in the original mixture.

By the application of this principle, which in the end amounts to the same thing as in the previously cited cases, it is possible to prepare gels having one or more of the heavy metallic oxides mixed with silica or similar substances. tioned examples, the necessary acid was derived from the hydrolysis of the stron ly hydrolyzed salts of heavy metals e. g. Al F Cl etc., while in the latter example the acid was supplied as such.

It is easily possible to reduce a mixture of certain of these oxides to a metallic state, and in this way obtain a mixture of silica and finely divided metal, the whole possessing a structure analagous to silica gel. For example, the following gels comprising silica and a' finely divided metal have been prepared, by reducing the corresponding metallic oxide gels with hydrogen at a low temperature:

Fe-I-SiO ou+sio,; Ni+SiO In the first men-' after being washed and dried may be the same chemically as the gel, but it does not have the same porous structure. The gel has much finer pores than the dried precipitate, and consequently the internal surface of the gel is many times as extensive as the internal surface of the dried precipitate. It is because of this extensive surface that these gels are so active catalytically. In preparing the gels the liquid after mixing should have an acid concentration of three tenths to nine-tenths gram ions of hydrogen per litre. The product of this invention is a hard glassy material having a porous structure substantially like that of silica gel and consisting of two or more colloidal oxides, or oxides and metals.-

From the foregoing it is appare'nt that according to the present invention it is possible to obtain hard adsorbent gels including a metal or metals or one. or more metallic oxides, this mixture being obtained from a metallic salt and a silicate. Furthermore it will be observed that while silica is a chemically inert substance, the metals and metallic oxides which are incorporated in the gel according to this invention are chemically active as compared to silica and also possess catalytic properties.

The term gel as used in the specification and claims designates a hard porous material having a porous structure similar to that of the silica gel obtained by the process described in Patent No. 1,297,724.

The term metal as used in the claims is not intended to include silicon and the term metal bearing material is used to designate a metal by itself as well as compounds thereof. 7

It is to be distinctly understood that any equivalent substance may be substituted for the sodium silicate and although the silicate has been referred to throughout the s ecification in connection with the preparat1on of the gel, this is merely illustrative of the class of substances that can be used to obtain the porous catalytic product of this invention.

Havin thus described the invention what is claime as new and desired to be secured by Letters Patent is:

1. The process of preparing a hard porous gel consisting in mixing in solution, a salt of a metal, an acid, and a substance which will react with the acid to produce a colloidal solution, said reagents being of such concentrations and proportions that neither gelatinization nor precipitation occurs immediately, butafter some time the entire "complete of about 0.3 to 0.9 gram ions of hydrogen per litre, whereupon, neither gelatinization nor precipitation occurs at once, but after some time the entire body of liquid hardens into a hydrogel, washing the hydro gel thus formed and thereafter removing moisture therefrom.

3. The process of preparing a hard po rous gel consisting in mixing solutions of a saltwof a metal, an acid, and a silicate which will react with the acid to produce a colloidal solution, said salt, acid, and silicate solutions being in proportions to give a concentration of acid after the reaction is com plete of about 0.3 to 0.9 gram ions of hydrogen per litre, whereupon, neither gelatmization nor precipitation occurs at once, but

after some time the entire body of liquid hardens into a hydrogel, washing the hydrogel thus formed and thereafter removing moisture therefrom.

4. The process of preparing a hard porous gel consistin in mixing solutions of a salt of a metal w 'ch is not easily hydrolyzed, an acid and a substance which will react with the acid to p'roducea colloidal solution, said salt, acid, and substance solutions'being in proportions to give a concentration of acid after the reaction is com:

plate of about 0.3 to 0.9 gram ionsof hydrogen per litre, whereupon, neither gelatlnization nor precipitation occurs at once but after some time the entire body of 11 uid hardens into a h drogel, washing the by rogel thus forme and thereafter removing moisture therefrom.

5. The process of preparing a hard pd rous gel consisting in mixing solutions of a nickle salt, an acid and a substance which will react with the acid to produce acolloidal solution, said salt, acid, and substance solutions being in roportions to give a concentration of acid after the reaction is complete of about 0.3 to 0.9 gram ions of hydrogen per litre, whereupon, neither gelaatinization nor precipitation occurs at once, but after some time the entire body of liquid hardens into a hydrogel, washing the hydrogel thus formed and thereafter removing moisture therefrom.

6. The process of preparing a hard porous gel consisting in mixing solutions of a nickle salt, an acid and a silicate which will react with the acid to produce a' colloidal solution, said salt, acid, and silicate solutions being in proportions to give a concentration of acid after the reaction is complete of about 0.3 to 0.9 gram ions of hydrogen per litre, tinization nor precipitation occurs at once, but after some time the entire body of liquid hardens into a hydrogel, washing the hydrogel thus formed and thereafter'removing moisture therefrom.

In testimony whereof I hereunto afix my signature.

WALTER A. PATRICK. 

